Enhancement of images in electron radiography

ABSTRACT

An X-ray system for producing visual images on a dielectric sheet by producing an electrostatic charge image on the sheet and then delivering oppositely charged particles to the charged sheet. Apparatus and process for increasing the electrostatic charge voltage between exposure and development, by producing the electrostatic charges in a high capacitance, low voltage configuration with the electrode and sheet in contact, and then converting to a low capacitance, high voltage configuration with the electrode and sheet spaced from each other prior to developing the visual image.

United States Patent 1191 Muntz et al.

[ Feb. 12, 1974 ENHANCEMENT OF IMAGES IN ELECTRON RADIOGRAPHY [75] Inventors: Eric P. Muntz, Pasadena; Murray S.

Welkowsky, Los Angeles, both of Calif. I

Primary Examiner-William F. Lindquist Attorney, Agent, or Firm-Harris, Kern, Wallen & Tinsley [57] ABSTRACT An X-ray system for producing visual images on a dielectric sheet by producing an electrostatic charge image on the sheet and then delivering oppositely charged particles to the charged sheet. Apparatus and process for increasing the electrostatic charge voltage V 2% between exposure and development, by producing the i g ZE electrostatic charges in a high capacitance, low volt- 1e 0 care g Configuration with the electrode and Sheet in contact, and then converting to a low capacitance, [56] References Cited high voltage configuration with the electrode and' UNITED STATES PATENTS sheet spaced from each other prior to developing the 2,825,814 3/1958 Walkup 250/65 X visual image. 2,802,948 8/1957 Vyverberg 2,711,481 6/1955 Phillips 250/65 8 Clams, 3 Drawing Flgllres I [I0 4 a 26 4/ 1 I 11 1 1 1 /7\ l I 30 /5 L\'\ \\\\\\\\\\\\\\\\\\\\\\f \\\\\\\\\\\\\\\\*\\\I\ 1 20' b 27 -32 a/ 27 L 2! ENHANCEMENT OF IMAGES IN ELECTRON RADIOGRAPI-IY This invention relates to X-ray systems and is particularly adapted for use with radiographic systems in which an X-ray source produces electrons and/or positive ions to form an electrostatic image suitable for printing. This type of radiographic system is sometimes referred to as ionography and utilizes a dielectric sheet as the recordmedium or receptor in place of the more conventional photographic film. The variation in X-ray intensity exiting from the object illuminated by the X-ray source produces a variation in electrostatic charge on the dielectric sheet. The electrostatic image on the dielectricsheet may then be converted to a visual image using conventional techniques such as the xerographic printing process. For further information on the basic ionographic system, reference may be made to a. the copending application entitled Radiographic- System with Xerographic Printing, Ser. No. 261,927 filed June 12, 1972 and assigned to the same assignee as the present application. The present application is directed to an improvement in handling of the dielectric sheet receptor during exposure and development to provide a darker visual image and shorter development times without significant degradation of the graphic techniques with the toner density being a function of the magnitude of the electrostatic charge on the receptor.

The electrostatic images formed on the receptor as a result of low incident X-ray dosage yield relatively low deposited charges, as compared to the charges of electrostatic images obtained in other systems such as the xero graphic system. Hence the resulting voltage on the receptor is relatively small. Low voltages are desirable during the exposure period in order to prevent a retarding field from building upon the receptor. Retarding fields on the receptor tend to inhibit the charge deposition process when operating in the high gain mode. Also, a high voltage deposited on the receptor at high gas pressure in the gap tends to cause breakdown when 'the pressure in the gap is reduced prior to removing the receptor from the exposure unit. For these reasons, it is highly advantageous to utilize an insulating receptor having high capacitance which yields a low image voltage on the receptor for a given charge deposition. The

voltage on the dielectric sheet is directly proportional to the charge and inversely proportional to the capacitance. j

The final optical density of the developed image on the receptor is proportional to the voltage and therefore high image voltages and a low capacitance for the receptor is indicated. The required development time also decreases with increasing voltage. Hence we find conflicting requirements of low voltage and high capacitance during exposure and high voltage and low capacitance during development.

It is an object of the presentiniventionto provide a new and improved process and apparatus for electrostatic imaging systems which provides for converting a dielectric sheet receptor from a high capacitance-condition to a low capacitance condition between the exposure and development steps to obtain the optimum features of both high and low capacitance receptors.

It is a specific object of the invention to provide such a system with the dielectric sheet receptor in contact with an electrode providing a high capacitance configuration for exposure and with the receptor spaced from the electrode providing'a low capacitance configuration for development.

Other objects, advantages, features and results will more fully appear in the course of the following description. The drawing merely shows and the description merely describes a preferred embodiment of the present invention which is given by way of illustration or example.

In the drawing:

FIG. 1 is a perspective view of an electrode-receptor unit incorporating the presently preferred embodiment of the invention;

FIG. 2 is a vertical sectional view through a cassette with the unit of FIG. 1 therein in the exposure configuration; and FIG. 3 is a vertical sectional view through a developing chamber with the unit of FIG. 1 therein in the developing configuration.

The electrode-receptor unit 10 of FIG. 1 includes a frame 11 defining an electrode space 12 therein. Means are provided for mounting a dielectric sheet 14 on the frame, the receptor sheet typically being a sheet of Mylar. In the embodiment illustrated, tension strips 15, 16 are carried at opposite sides of the frame 11. A plurality of bosses 17 project from each of the tension strips 15, 16 for engaging corresponding openings in the sheet 14. Interengaging elements may be provided on the frame and strip for guiding movement of the strip toward and away from the frame. Referring to FIG. 2, a pin 20 carried on the frame projects into an opening 21 in the strip, with a compression spring 22 disposed about the pin 20 in a counterbore in the strip forurging 1 the strip away from the frame. A plurality of the pins 20 may be provided for each tension strip.

An electrode 25 is carried in the frame 11. The frame and electrode have interengaging elements which permit relative movement of frame and electrode, and in the embodiment illustrated, opposingribs 26 of the electrode 25 project into corresponding slots 27 of the frame.

In the exposure configuration of FIG. 2, the dielectric sheet 14 is placed on the frame by engaging the bosses 17 with openings in the sheet. The electrode-receptor unit 10 is slid into the exposure cassette or box 30 through an access door at the side (not shown). The cassette 30 may be conventional in design with aluminum or steel bottom and sides and a top 31 of beryllium or other material having low X-ray absorption. An insu- FIG. 2, the electrode 25 is the anode and is connected to the positive side ofa voltage source 33, with the top 31 serving as the cathode and connected to the negative side ofthe source 33. The frame 11 is an insulator.

In the condition illustrated in FIG. 2 with the rceptor 14 in contact with the electrode 25, the receptor has a high capacitance resulting in a relatively low voltage on the receptor for a given charge deposition. The upper surface of the electrode 25 preferably is convex to provide contact between the receptor and electrode over the entire surface of the electrode. Typically with an electrode in the order of inches X 14 inches, the center may be five-thousandths of an inch higher than the edges of the electrode.

After the exposure, the electrode-receptor unit 10 is removed from the cassette and placed in a developing chamber 40. Any of the presently available developing chambers may be utilized, including those shown in U.S. Pat. Nos. 3,648,901 and 3,646,910 and the patents cited therein. The unit 10 preferably is mounted at the top of the developing chamber 40 and in the embodiment illustrated, a tongue and groove arrangement is utilized for lateral sliding insertion and support. A T- groove 41 in the anode engages a mating T rib 42 in the top of the chamber 40. A clearance opening 41' is provided in the side of the frame 11.

When the unit 10 is inverted from the position of FIG. 2 to the position of FIG. 3; the frame moves downward relative to the electrode providing an air space between the electrode and receptor.

When in the developing configuration of FIG. 3, the receptor has a relatively low capacitance and hence an increase in the image voltage on the receptor. A quantity of developing powder is introduced into the developing chamber through the inlet line 44 and positive charged particles of developing powder are attracted to the negatively charged receptor. The optical density of the deposited developing powder is a function of the voltage of the charges on the receptor. Also, the developing time is shorter for higher voltage images, all other factors remaining constant. The unit is removed from the developing chamber and the powder particles on the receptor are fixed in the conventional manner providing the completed X-ray picture.

By lifting the receptor from the electrode between the exposure and developing steps, the capacitance of the receptor is decreased in proportion to the ratio of the distance oflift to the receptor thickness, with a corresponding increase in the image voltage on the receptor. By way of example, an order of magnitude increase in darkening of the visual image can be obtained with a lift or spacing between electrode and receptor of three-eighths inch, without noticeable degradation of the resultant image, for a receptor four thousandths of an inch thick.

We claim:

1. In an X-ray system having an exposure unit for formation of an electrostatic image on exposure to X-rays, and a developing unit for formation of a visual image, the combination of:

an electrode; and

means for supporting said carrier in said exposure unit with said. receptor at said electrode, and supporting said carrier in said developing unit with said receptor maintained uniformly spaced from said electrode a predetermined distance during developing.

2. The system as defined in claim 1 wherein said supporting means includes a support member with said electrode and said receptor mounted thereto, with one of said electrode and receptor movable relative to the other in said support member.

3. An electrode-receptor unit for an X-ray electrostatic imaging system, comprising:

a frame member;

means for'mounting a dielectric sheet receptor on said frame member; and

an electrode mounted in said frame member and movable between a first position for contacting said receptor and a second position uniformly spaced from said receptor a predetermined distance.

4. A unit as defined in claim 3 wherein said frame member defines an electrode space and said receptor is mounted across said space and said electrode is mounted in said space. i

5. A unit as defined in claim 3 wherein said mounting means includes:

a strip member engageable with said receptor at an edge thereof;

interengageable means on said frame member and strip member for movement of said strip member toward and away from said frame member; and resilient means urging said strip member away from said frame member for tensioning said receptor.

6. A unit as defined in claim 5 wherein said frame member and electrode include first and second interengageable stop means defining first and second positions, respectively, with said electrode slidable in said frame member between saidfirst position in contact with said receptor and said second position spaced from said receptor.

7. A unit as defined in claim 3 wherein said frame member and electrode include first and second interengageable stop means defining first and second positions, respectively, with said electrode slidable in said frame member between said first position in contact with said receptor and said second position spaced from said receptor.

8. In an X-ray imaging process, the steps of:

positioning a dielectric sheet receptor in a gap between a pair of electrodes and in contact with one of the electrodes; producing an electrostatic charge of relatively low voltage on the receptor by applying an electrical potential across the electrodes and directing X-rays into the gap;

converting the relatively low voltage charge on the receptor to a relatively high voltage charge by moving the receptor away from the one electrode a predetermined distance with the receptor and one electrode uniformly spaced; and

producing a visual image on the receptor by delivering oppositely charged particles to the charged receptor while maintaining the receptor uniformly spaced from the one electrode.

a m a: k 

1. In an X-ray system having an exposure unit for formation of an electrostatic image on exposure to X-rays, and a developing unit for formation of a visual image, the combination of: a dielectric sheet receptor; a receptor carrier for carrying said receptor thereon; an electrode; and means for supporting said carrier in said exposure unit with said receptor at said electrode, and supporting said carrier in said developing unit with said receptor maintained uniformly spaced from said electrode a predetermined distance during developing.
 2. The system as defined in claim 1 wherein said supporting means includes a support member with said electrode and said receptor mounted thereto, with one of said electrode and receptor movable relative to the other in said support member.
 3. An electrode-receptor unit for an X-ray electrostatic imaging system, comprising: a frame member; means for mounting a dielectric sheet receptor on Said frame member; and an electrode mounted in said frame member and movable between a first position for contacting said receptor and a second position uniformly spaced from said receptor a predetermined distance.
 4. A unit as defined in claim 3 wherein said frame member defines an electrode space and said receptor is mounted across said space and said electrode is mounted in said space.
 5. A unit as defined in claim 3 wherein said mounting means includes: a strip member engageable with said receptor at an edge thereof; interengageable means on said frame member and strip member for movement of said strip member toward and away from said frame member; and resilient means urging said strip member away from said frame member for tensioning said receptor.
 6. A unit as defined in claim 5 wherein said frame member and electrode include first and second interengageable stop means defining first and second positions, respectively, with said electrode slidable in said frame member between said first position in contact with said receptor and said second position spaced from said receptor.
 7. A unit as defined in claim 3 wherein said frame member and electrode include first and second interengageable stop means defining first and second positions, respectively, with said electrode slidable in said frame member between said first position in contact with said receptor and said second position spaced from said receptor.
 8. In an X-ray imaging process, the steps of: positioning a dielectric sheet receptor in a gap between a pair of electrodes and in contact with one of the electrodes; producing an electrostatic charge of relatively low voltage on the receptor by applying an electrical potential across the electrodes and directing X-rays into the gap; converting the relatively low voltage charge on the receptor to a relatively high voltage charge by moving the receptor away from the one electrode a predetermined distance with the receptor and one electrode uniformly spaced; and producing a visual image on the receptor by delivering oppositely charged particles to the charged receptor while maintaining the receptor uniformly spaced from the one electrode. 